Sure it can. If he signed stickers prior to signing his WWE contract then the contract doesn't come into play. Or if his special contract allows him to do things like this (sign stickers), then it's a non-issue as well. Notice he's still able to advertise on his trunks, very few dates on his contract, etc.? No telling what all special stipulations he's got in his contract. Moot point if he signed the stickers prior to signing with WWE again though.